PREVALENCE OF BORRELIA-BURGDORFERI (SENSU-LATO) IN IXODES-RICINUS (L)POPULATIONS IN FRANCE, ACCORDING TO A PHYTOECOLOGICAL ZONING OF THE TERRITORY

Ixodes ricinus is considered as the main vector of Lyme Borreliosis in France. The aim of our investigations was to obtain a comprehensive v iew of the spatial risk linked to the distribution of the species in o ur country. Previous studies [1] have provided strong evidence that th e species populations are widely distributed, so the objective of the present work was to ascertain the bacteriological infection of the tic k by the agent of the zoonosis (Borrelia burgdorferi, sensu late), ove r the French territory, whatever the ecological conditions may be. For this purpose, we kept the same framework as that used in our acarolog ical investigation, a phytoecological zoning of the territory into 54 geographically separate and ecologically distinct units distributed in to three climatic zones. Batches of ticks, picked up in these differen t phytoecological units (only two thirds of which were sampled), were submitted for bacteriological investigation. A total of 4,673 ticks we re examined, individually, for the presence of Borellia burgdorferi, b y immunofluorescence. Percentages of infection according to the variou s stages of Ixodes ricinus free stages, collected by flagging, were as follows: 4.95% in 3,247 nymphs, 11.2% in 699 males, 12.5% in 727 fema les. Larvae were ignored. Practically all the tested units harboured t he bacterium. The percentage of tick samples (25 ticks or more) absolu tely free of Borrelia, wherever they came from, is very low (not excee ding 10 percent of the sampled forests). Our study confirms the assess ment of a widespread distribution of the zoonosis in France which was, until now, exclusively based on an approximate distribution of limite d human cases observed in the country.